The involvement of alternative DNA structures in chromosome translocations and other rearrangements has gained attention in recent years. One type of alternative structure, a cruciform, has been demonstrated to form at DNA sequences that comprise a palindrome in vitro. While strong evidence causally implicates long palindromic DNA sequences with heritable reciprocal translocations in humans, whether palindromes contribute to translocation in cells other than germ cells has not been demonstrated. The possibility is particularly relevant in the case of T and B lymphoid cells where there are extra demands placed upon accurate DNA metabolism during differentiation, and where, although translocation is a marked feature in tumors of the lymphoid system, the underlying errors have been only partially defined. The purpose of the present study is to test the notion that (long) DNA palindromes can instigate translocation in pro/pre B cells. The relationship between palindromy and translocation in mouse pro B cell lines (transformed by Abelson murine leukemia virus), and in a human pre-B line, Nalm6, will be investigated. A recently developed method for characterizing translocation at a genome-wide level will be employed. These studies may establish a new category of endogenously generated DNA damage with significance in tumorigenesis and other pathologies in the lymphoid system and beyond.